Many medical diagnostic, surgical and interventional procedures rely on imaging tools to provide information descriptive of status of visually perceived representations of portions or organs of a patient. In part as a result of increasing sophistication of medical tools in general, and imaging apparatus in particular, more types of imaging devices are being adapted for application in the context of medical diagnostics and procedures.
In many instances, medical tools capable of rendering images of organs or tissues have found great utility and have been adapted to facilitate a broad variety of medical needs. These applications have resulted in development of a gamut of specialized imaging tools, including X-ray, CT and fluoroscopic visualizing aids, and many different types of optical imaging devices.
In many imaging applications, pixelated detectors are increasingly employed to realize electronic digital representations of image data. Some types of systems employ an array of scintillation cells and an associated array of photodiodes formed from a sheet of semiconductive material, where the scintillation material in each cell converts incident X-radiation to visible photons suitable for detection by the one diode in the array that is intended to be optically coupled to that cell. Mechanisms which degrade the signals from the diode array can cause machine-to-machine data instability, or reduce measurement or imaging repeatability, and may give rise to data distortion causing imaging defects such as ring artifacts, bands or smudges in the resultant data, when it is employed to form a visible image, or engender inaccuracy and/or reduced repeatability in the context of automated characterization of tissues.
In turn, digital techniques provide great imaging flexibility, such as, for example, overlay or direct comparison, on the fly, of various aspects and views from various times. For example, pre-surgery images can be available, in real time, in the operating room scenario, for comparison to images reflective of the present status of the same tissues. Many other types of special-purpose enhancements are now also possible. In some instances, imaging aids, such as contrast-enhancing agents, are introduced into the subject or patient to aid in increasing available data content from the imaging technique or techniques being employed.
However, regulatory changes, increasingly sophisticated measurement needs and other factors combine to place new demands on pixelated detectors for computed tomography applications, among others. Recent desire to even further reduce the total dose of X-radiation delivered to the subject, to reduce the energy of the X-rays on a per-photon basis and to achieve increased contrast parameters within the resulting images collectively demand greater linearity and sensitivity of the photodetector arrays used in such visualization tools, together with reduced image noise and artifacts of various sorts.
Signal artifacts resulting from the photodetector array itself also may pose some fundamental limits on overall system performance. Examples of mechanisms known to potentially give rise to crosstalk artifacts include: (i) charge carriers generated in one diode resulting in a signal in another diode, via carrier diffusion and/or inter-diode capacitance; (ii) scattering of X-rays from one scintillator cell to a neighboring scintillator cell, followed by conversion to a photon and detection of that photon by a diode coupled to the neighboring cell; (iii) leakage of light from a scintillator cell to a photodiode associated with another scintillator cell; and (iv) scattering of photons generated in the target scintillator cell into a neighboring scintillator cell through intercell septa, and thus to a photodiode associated with the neighboring cell. In many situations, where photodiodes are co-fabricated on a common substrate, diffusion of carriers from one photodiode to another contribute a dominant component to interdiode crosstalk.
In turn, these various artifacts present characteristics which vary linearly and nonlinearly with both X-ray fluence and operating parameters. Additionally, achieving alignment of the scintillator cell array with the photodiode array presents difficulty in manufacturing, with unwanted signal characteristics or artifacts being associated with residual imprecision in that process.
For the reasons stated above, and for other reasons discussed below, which will become apparent to those skilled in the art upon reading and understanding the present disclosure, there are needs in the art to provide improved photodiode/scintillator photodetectors in support of increasingly stringent and exacting performance and economic standards in settings such as medical imaging.